CVE-2021-46984— kyber: fix out of bounds access when preempted
Quick assessment
Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于抢占时的越界访问。
Possible ATT&CK Techniques 1 AI
T1059 · Command and Scripting InterpreterAffected Version Matrix 12
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Linux | Linux | a6088845c2bf754d6cb2572b484180680b037804< 0b6b4b90b74c27bea968c214d820ba4254b903a5 |
affected |
a6088845c2bf754d6cb2572b484180680b037804< 54dbe2d2c1fcabf650c7a8b747601da355cd7f9f |
affected | ||
a6088845c2bf754d6cb2572b484180680b037804< a287cd84e047045f5a4d4da793414e848de627c6 |
affected | ||
a6088845c2bf754d6cb2572b484180680b037804< 2ef3c76540c49167a0bc3d5f80d00fd1fc4586df |
affected | ||
a6088845c2bf754d6cb2572b484180680b037804< efed9a3337e341bd0989161b97453b52567bc59d |
affected | ||
4.18 |
affected | ||
< 4.18 |
unaffected | ||
5.4.120≤ 5.4.* |
unaffected | ||
| … +4 more rows | |||
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I. Basic Information for CVE-2021-46984
Vulnerability Information
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Vulnerability Title
kyber: fix out of bounds access when preempted
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved:
kyber: fix out of bounds access when preempted
__blk_mq_sched_bio_merge() gets the ctx and hctx for the current CPU and
passes the hctx to ->bio_merge(). kyber_bio_merge() then gets the ctx
for the current CPU again and uses that to get the corresponding Kyber
context in the passed hctx. However, the thread may be preempted between
the two calls to blk_mq_get_ctx(), and the ctx returned the second time
may no longer correspond to the passed hctx. This "works" accidentally
most of the time, but it can cause us to read garbage if the second ctx
came from an hctx with more ctx's than the first one (i.e., if
ctx->index_hw[hctx->type] > hctx->nr_ctx).
This manifested as this UBSAN array index out of bounds error reported
by Jakub:
UBSAN: array-index-out-of-bounds in ../kernel/locking/qspinlock.c:130:9
index 13106 is out of range for type 'long unsigned int [128]'
Call Trace:
dump_stack+0xa4/0xe5
ubsan_epilogue+0x5/0x40
__ubsan_handle_out_of_bounds.cold.13+0x2a/0x34
queued_spin_lock_slowpath+0x476/0x480
do_raw_spin_lock+0x1c2/0x1d0
kyber_bio_merge+0x112/0x180
blk_mq_submit_bio+0x1f5/0x1100
submit_bio_noacct+0x7b0/0x870
submit_bio+0xc2/0x3a0
btrfs_map_bio+0x4f0/0x9d0
btrfs_submit_data_bio+0x24e/0x310
submit_one_bio+0x7f/0xb0
submit_extent_page+0xc4/0x440
__extent_writepage_io+0x2b8/0x5e0
__extent_writepage+0x28d/0x6e0
extent_write_cache_pages+0x4d7/0x7a0
extent_writepages+0xa2/0x110
do_writepages+0x8f/0x180
__writeback_single_inode+0x99/0x7f0
writeback_sb_inodes+0x34e/0x790
__writeback_inodes_wb+0x9e/0x120
wb_writeback+0x4d2/0x660
wb_workfn+0x64d/0xa10
process_one_work+0x53a/0xa80
worker_thread+0x69/0x5b0
kthread+0x20b/0x240
ret_from_fork+0x1f/0x30
Only Kyber uses the hctx, so fix it by passing the request_queue to
->bio_merge() instead. BFQ and mq-deadline just use that, and Kyber can
map the queues itself to avoid the mismatch.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于抢占时的越界访问。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2021-46984
| # | POC Description | Source Link | Shenlong Link |
|---|
AI-Generated POC
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Other References for CVE-2021-46984 (5)
Same Patch Batch · Linux · 2024-02-28 · 86 CVEs total
| CVE-2021-47013 | 9.8 CRITICAL | net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send |
| CVE-2021-46999 | 9.8 CRITICAL | sctp: do asoc update earlier in sctp_sf_do_dupcook_a |
| CVE-2021-47036 | 9.8 CRITICAL | udp: skip L4 aggregation for UDP tunnel packets |
| CVE-2021-47017 | 8.8 HIGH | ath10k: Fix a use after free in ath10k_htc_send_bundle |
| CVE-2021-47035 | 8.8 HIGH | iommu/vt-d: Remove WO permissions on second-level paging entries |
| CVE-2021-47049 | 8.4 HIGH | Drivers: hv: vmbus: Use after free in __vmbus_open() |
| CVE-2021-47014 | 7.8 HIGH | net/sched: act_ct: fix wild memory access when clearing fragments |
| CVE-2021-46998 | 7.8 HIGH | ethernet:enic: Fix a use after free bug in enic_hard_start_xmit |
| CVE-2021-47048 | 7.8 HIGH | spi: spi-zynqmp-gqspi: fix use-after-free in zynqmp_qspi_exec_op |
| CVE-2021-46992 | 7.8 HIGH | netfilter: nftables: avoid overflows in nft_hash_buckets() |
| CVE-2020-36785 | 7.8 HIGH | media: atomisp: Fix use after free in atomisp_alloc_css_stat_bufs() |
| CVE-2021-46993 | 7.8 HIGH | sched: Fix out-of-bound access in uclamp |
| CVE-2021-47040 | 7.8 HIGH | io_uring: fix overflows checks in provide buffers |
| CVE-2021-46977 | 7.8 HIGH | KVM: VMX: Disable preemption when probing user return MSRs |
| CVE-2021-47012 | 7.8 HIGH | RDMA/siw: Fix a use after free in siw_alloc_mr |
| CVE-2021-47011 | 7.8 HIGH | mm: memcontrol: slab: fix obtain a reference to a freeing memcg |
| CVE-2020-36787 | 7.8 HIGH | media: aspeed: fix clock handling logic |
| CVE-2021-47041 | 7.5 HIGH | nvmet-tcp: fix incorrect locking in state_change sk callback |
| CVE-2021-47001 | 7.5 HIGH | xprtrdma: Fix cwnd update ordering |
| CVE-2021-46983 | 7.5 HIGH | nvmet-rdma: Fix NULL deref when SEND is completed with error |
Showing top 20 of 86 CVEs. View all on vendor page → →
IV. Related Vulnerabilities
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Same vendor: Linux
-
CVE-2026-98384
bpf: Fix out-of-bounds read of sk_protocol in bpf_sock_destr -
CVE-2026-98383
bpf: Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL -
CVE-2026-98382
bpf: Reject dev-bound-only programs on other devices -
CVE-2026-98381
veth: manage XDP program pointers during channel resize -
CVE-2026-98380
net/sched: reject IDR error pointers when deleting actions
V. Comments for CVE-2021-46984
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